A. Pornon et al., GROWTH-RATES AND NUTRITION STATUS OF AN OPEN AND A CLOSED POPULATION OF RHODODENDRON-FERRUGINEUM L IN THE NORTHWESTERN ALPS (FRANCE), Trees, 11(2), 1996, pp. 91-98
This study evaluates the utility of cell compounds as indicators of nu
trition status of plant populations. An overview of the soluble free a
mino-acids, carbohydrates and P-compounds in the two year classes of l
eaves from Rhododendron ferrugineum populations showing variable biolo
gical performances, was drawn up using carbon-13 and phosphorus-31 nuc
lear magnetic resonance spectroscopy (NMR). The results showed differe
nces between the age of leaves and the degree of population closure. T
he open population, which has the smallest growth rate and net primary
productivity, had generally lower levels of aminoacids but higher lev
els of carbohydrates and P-compounds. Neither the amounts of mineral n
itrogen produced by the soils nor the total nitrogen concentrations in
leaves differed significantly. Still we hypothesize that the nitrogen
avail ability could be largely responsible for the variations observe
d between the populations, as phosphorus analyses showed that the two
populations did not suffer significant P deficiencies. Differences in
vitality of R. ferrugineum may be explained by the fact that in an ope
n population R. ferrugineum is forced into a situation of sharing nutr
ients with other species while in a closed population it is the sole s
pecies to exploit a specific pool of nutrients. Finally we observed th
at the C-13- and P-31-NMR approach is more suitable for studying the n
utrition status of plant populations under field conditions than the d
etermination of the total amounts of different elementary nutrients.